1. Field of the Invention
The present invention relates to an ink head to be mounted to an ink jet printer.
2. Description of the Related Art
There have been known various types of image recording apparatuses. In recent years, the ink jet printers adopting an ink jet recording system as the image recording apparatus have come into wide use. The reason why is because the ink jet printers are relatively low-priced and small-sized.
There are various kinds of ink jet printers. For example, the ink jet printer has an ink head. Alternatively, the ink jet printer has an ink head and a moving mechanism. Alternatively, the ink jet printer has an ink head, a moving mechanism and a conveying mechanism.
The ink head jets ink toward a recording medium in which an image is recorded. The moving mechanism moves the ink head relative to the recording medium. The conveying mechanism moves the recording medium relative to the ink head.
The ink head has an ink head module and a nozzle plate. The ink head module has a longitudinal central axis. The ink head module has a plurality of ink chambers which are arranged so as to be separated from one another at predetermined pitches along the longitudinal central axis thereof. The nozzle plate is arranged on the surface (front surface) of the ink chamber opposing to the recording medium.
The nozzle plate has nozzles, which allow ink to pass through each of the plurality of ink chambers. Each ink chamber has known jetting energy generating means such as, for example, a piezo element. The jetting energy generating means applies a force necessary for jetting to ink at the time of ink jetting. Each ink chamber has known jetting energy generating means (jetting energy element), thereby an ink droplet can be jetted from the nozzle.
The above described ink jet printer intermittently conveys the recording medium by driving of the conveying mechanism. During the intermittent conveying operation, the ink jet printer drives the ink head while the recording medium is at a standstill. At the same time, the ink jet printer jets the ink droplet from a plurality of nozzles. By these operations, the ink jet printer records a desired image on the recording medium. That is, the ink jet printer puts the ink jetted from the nozzle on the recording medium. The ink jet printer forms an image by this putted ink.
As described above, the ink jet printer records an image by jetting ink from the nozzle. Accordingly, when a flying direction of the jetted ink droplet changes from a desired direction, the ink droplet puts on a position, which is deviated from a predetermined putting position on the recording medium. When the flying direction changes as described above, the jetted ink droplet sometimes coalesces into the ink droplet jetted from the adjacent nozzle during the flying. In this case, the recorded image is deteriorated in quality.
In the ink head, the ink droplet sometimes puts on the front surface of the nozzle plate. For example, the ink droplet jetted from the nozzle and/or the ink droplet jetted/sucked after the maintenance work of the ink head puts on the front surface of the nozzle plate.
The ink droplet put on the front surface is referred to as “put-ink-droplet” in the present specification. The put-ink-droplet stays in the vicinity of a nozzle opening. For this reason, the put-ink-droplet has a risk of being brought into contact with the ink to be jetted from the nozzle. When the ink to be jetted is brought into contact with the put-ink-droplet, a remarkable deviation occurs in the flying direction of the jetted ink droplet. That is, the jetted ink droplet causes a flying deflection. For this reason, there are available those ink heads, which have the nozzle plate subjected to water repellent process on the entire surface so that the put-ink-droplet does not stay in the vicinity of the nozzle opening. However, when such a water repellent process is applied to the front surface of the nozzle plate, it is easy for the put-ink-droplet to move on the front surface. Accordingly, the put-ink-droplet moves to the vicinity of the opening of the nozzle. And the put-ink-droplet moves to the vicinity of the opening of the other nozzle than the nozzle. For this reason, the put-ink-droplet in the vicinity of the opening and the ink to be jetted have a possibility of coming in contact with each other. In this way, even when the water repellent process is applied to the entire surface of the front surface of the nozzle plate, the ink head still has a possibility that the jetted ink droplet causes the flying deflection.
In recent years, the ink jet printers have been expected to speed up the image forming speed and highly increase the density of recording density. Hence, the ink head has a plurality of nozzles for each ink chamber. Such an ink jet printer can increase the number of nozzles without increasing the number of ink chambers. Accordingly, such an ink jet printer can enhance the recording density. However, in such an ink head, when there is an irregularity in accuracy for making nozzle, it is difficult to arrange each nozzle 131 ideally as shown in FIG. 9A.
For example, an ink head 110 shown in FIGS. 10A and 10B, has two each nozzle 131 for each ink chamber 120. These nozzles 131 have a front-surface-opening, which is an opening at the front surface side of the nozzle plate, and a rear-surface-opening which is an opening at the ink chamber side. Each nozzle 131 is formed closely to the adjacent nozzle 131. Therefore, when there is an irregularity in the accuracy for making nozzle, a portion of the rear-surface-opening of one nozzle 131 and a portion of the rear-surface-opening of the other adjacent nozzle 131 overlap with each other. Each nozzle 131, as shown in FIGS. 11A and 11B, sometimes has a portion of the rear-surface-opening overlapped with side walls 121. In this way, each nozzle 131 interferes with the other nozzle and the side wall as shown in FIG. 10B and FIG. 11B. As a result, two ink droplets 80 jetted from the ink head 110 cannot jet in a desired jetting direction. In other words, the ink droplet to be jetted from the ink head 110 causes the flying deflection. Therefore, the two ink droplets 80 have a risk of being not put on a desired position on the recording medium. Further, the two ink droplets 80 have a risk of coalescing with each other during the flying. Note that, ideally speaking; the two ink droplets fly without coalescing with each other as shown in FIG. 9B.